The present invention relates to hydraulic systems of the type used to actuate machinery. More specifically, the present invention relates to controlling such systems through measurement of position, velocity, acceleration, and/or direction of movement of hydraulic actuator pistons of hydraulic actuators.
Hydraulic systems are used in a wide variety of industries ranging from road construction to processing plants. These systems are generally formed of hydraulic control valves and hydraulic actuators. Typical hydraulic actuators include a hydraulic cylinder containing a piston. A rod is attached to the piston at one end and to an object, which is to be manipulated by the hydraulic actuator, at the other end. The hydraulic system controls at least one hydraulic control valve to direct a hydraulic fluid flow into and out of at least one cavity of a hydraulic actuator that is defined by the piston and the hydraulic cylinder. The hydraulic fluid flow causes a change in the position of the piston within the hydraulic cylinder and produces the desired actuation of the object.
The control of the hydraulic actuators is often performed by an operator who visually inspects the position of the hydraulic actuators. Such a physical inspection is relatively crude and prone to a great deal of inaccuracy. For many applications, it would be useful to know the position, velocity and/or acceleration of the piston. By these variables, a control system could be established to more precisely control the location or orientation, velocity and acceleration of the objects being actuated by the hydraulic actuators. For example, a blade of a road grading machine could be repeatedly positioned as desired resulting in more precise grading.
There is a need for improved methods and devices which are capable of achieving accurate, repeatable, and reliable hydraulic actuator piston position measurement and control.
The present invention is directed to a hydraulic control system for controlling at least one hydraulic actuator. The hydraulic control system includes a fluid flow sensor, a controller, and a communication link. The flow sensor is positioned in line with a hydraulic fluid flow and is adapted to measure a flow rate of the hydraulic fluid flow traveling into and out of a cavity of the hydraulic actuator. The flow sensor includes a sensor signal that is related to a position, velocity, acceleration, and/or a direction of movement of a piston contained in a hydraulic cylinder of the hydraulic actuator. A hydraulic control valve controls the hydraulic fluid flow traveling into the cavity, the volume of which is directly related to the position of the piston. The controller is adapted to receive the sensor signal from the flow sensor through the communication link.
In one aspect of the invention, the controller provides a piston information output relating to various types of piston information. The piston information generally corresponds to the position, velocity, acceleration, and/or the direction of movement of the piston. The piston information output can be provided to a human-machine interface to aid in the control of the piston and, thus, the object being actuated by the actuator.
In another aspect of the present invention, the controller produces a control signal based upon a comparison of the sensor signal to a reference signal. The reference signal generally relates to a desired position, velocity, acceleration, and/or direction of movement of the piston. The control signal is used to control the hydraulic fluid flow such that the piston is adjusted toward the desired position, velocity, acceleration, and/or direction of movement.
The present invention is also directed toward a method of controlling at least one piston of a hydraulic actuator. Here, a flow rate of a hydraulic fluid flow traveling into and out of a cavity of the hydraulic actuator is measured. Piston information relating to at least one of a position, a velocity, an acceleration, and a direction of movement of the piston is then calculated based upon the measured flow rate. Next, a reference signal is provided, which relates to at least one of a desired position, velocity, acceleration, and/or a direction of movement of the piston. Finally, the hydraulic fluid flow is adjusted based upon a comparison between the piston information and the reference signal. In this manner, the piston, whose movement is directly related to the hydraulic fluid flow, can be adjusted toward the desired position, velocity, acceleration, and/or direction of movement that is desired.